Impact mill



United States Patent 7/1958 Adams 2,917,248 12/1959 Krug..........2,981,490 4/1961 0 241/275 24l/299X 241/275 241/275 241/55 241/275X241/275 onley......... 3,023,973 3/1962 Conley...... 3,149,790 9/1964Hoffstrom. 3,171,604 3/1965 Conley...... 3,258,211 6/1966 Behnke.......

Primary Examiner-Robert C. Riordon Assistant Exam iner- [72] lnventorJohannes F. E. Kampe Torrance, California [21] Appl. No. 693,561

[22] Filed Dec. 26, 1967 [45] Patented Dec. 1, 1970 [73] AssigneeMcDonnell Douglas Corporation a corporation of Maryland Donald G. Kelly[54] IMPACT MILL Attorney strauch, Nolan, Neale, Nies & Kurz 4 Claims, 4Drawing Figs.

1,857,539 5/1932 l-ladsel....................,..... 241/275 away fromthe rotor periphery.

Patentgd Dec. 1, 1970 INVENTOR Johannes FE Kampe Om m w x om Nm y m/ mo9 w. ow van. 8 9

QNNMVN NM- Patented Dec. 1, 1970 Shoot INVENTOR Johannes FE KampeATTORNI IMPACT MILL BACKGROUND or THE INVENTION This invention relatesgenerally to material grinding and comminuting apparatus, and moreparticularly to a comminuting device of the impact type.

In the past machines of various types including ball mills, hammermills, impact mills, and jet mills have been used to effect comminutionof particles. Each of these'types has its advantages and associateddisadvantages. Most of these prior art devices have been veryinefficient in that they are generally designed to impart turbulence andmore than one impact or breaking force to a particle, thus wastingavailable energy. Additionally, the hammer, impact, and jet millsnormally pump an excessive amount of fluid, thus requiring a high inputener-' The efficiency of apparatus of this type is generally determinedby relating the required input energy to the degree of reduction inparticle size as measured by the amount of new specific surfacecreated,ge'nerally expressed in cm per gram. Thus, to obtain maximumefficiency, it is desirable to direct all input energy toward creatingnew specific surface. and to minimize energy losses due to turbulence,friction, and excessive air flow.

One prior proposal to accomplish this is disclosed in U.S. Pat. No.3,149,790. While thisdevice performed substantially better than otherknown apparatus, nevertheless, it was subject to wear particularly alongthe trailing walls of the rotor channels through which the materialpassed for delivery to the impact area, thus requiring premature andfrequent replacement of the wall liners. Additionally, the surface areawear on the impact targets was unduly concentrated. Also wear occurredat the periphery of the rotor because of splashback of the particles andimpingement on the rotor after they struck the target impact surfaces.

SUMMARY OF THE INVENTION It is a primary object of this invention toprovide a novel comminuting apparatus having an extended service lifeover whichfull efficiency of operation is maintained.

It is another object of this invention to provide a novel comminutingapparatus in which wear is substantially reduced and generally confinedto readily-replaceable parts.

It is another object of this invention to provide a novel impact millhaving impact targets so arranged with respect to a particleaccelerating rotor to prevent impingement of the crushed particles onthe rotor periphery, thus reducing rotor wear.

It is another object of this invention to provide a novel impact millhaving a rotor with radial channels lined with wear surfaces, thesurfaces being so shaped to spread the material uniformly thereover andthus prevent concentrated wear on the surfaces and the impact targets onwhich the material imp- Inges.

In summary, this invention accomplishes the above objects and overcomesthe disadvantages of the prior art devices by providing an impact millhaving a rotor with radially extending channels therein which connects acenter annular chamber, to which material is fed, with an impact chambercontaining an impact target device. The walls of the channels are linedwith replaceable U-shaped wear strips which have a flat-bottomed wearingsurface across which the particles are uniformly distributed duringrotation of the rotor. The flat-bottomed surface prevents concentratedwear of the strips and also promotes uniform wear across the impactsurfaces of the target device. The impact target device comprises aplurality of individual targets carried by upper and lower rings andspaced from each other to providea passage between adjacent targets forescape of the crushed material from the targetimpact surface. The impactface of each target is so positioned with respect to the trajectory ofthe material leaving the rotor channels, as to cause the material toflow radially outwardly away from the rotor periphery after it strikesthe target surface without loss of impact efficiency. Also, pressurizedair is introduced above and below the rotor and directed radiallyoutwardly into the impact chamber to prevent crushed material fromentering the rotor and bearing areas.

Additional objects and advantages will become apparent as thedescription proceeds in connection with the accompanying drawings.

THE DRAWINGS FIG. 1 is a front'elevation .view of the comminutingapparatus, partially in section, along line 1-1 of FIG. 2;

FIG. 2 is a top fragmentary view of the apparatus of FIG. 1 partiallyin'section, showing the spaced arrangement of the impact targets and theradiallyextending channels connecting the material inlet funnel androtor center to the target chamber; p

FIG. 3 is an enlarged sectional view of the radial .channel and its wearliner taken along line 3-3 of FIG. 2; and

FIG. 4 is an enlarged fragmentary view of the impact or target area.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now more particularlyto the drawings, the apparatus of the present invention includes a standor base 10 supporting a rotor housing 12 and a motor housing 14 insideby-side relation. The stand is provided with adjustable legs 16 toprovide accurate leveling of the assembly.

At its upper end the housing 12 is closed by a cover plate 18 held inplace against an annular shoulder 20 on the housing wall by a snap ring21. The top wall 18 carriesa central conical material inlet funnel 22carrying an extension 24 leading into a rotor chamber 26 formed betweenthe top wall 18 and a horizontal wall 28, preferably formed integrallywith the housing 12.

The wall 28 carries a downwardly projecting hub 30 formed centrally ofthe housing which supports upper and lower bearings 32 and 34 separatedby a spacer collar 36. The bearings rotatably support a rotor shaft 38,the upper end of which carries rotor-assembly 40 inthe rotor chamber-26and the lower end of which carries a pulley 42. The motor pulley 44 isdrivingly connected to the rotor pulley 42 by a belt 46 which passesover an 'idlerpulley 48 suitably supported on the outer end of an arm 50projecting from a collar 52 held in placeon the hub 30 by a snap ring54.

The rotor assembly 40 includes upper and lower plate members 56 and 58,respectively, preferably secured together by screws 60 extending througha discontinuous peripheral flange 62. To impart additional structuralrigidity to the assembly the upper rotor plate 56 is provided with adiscontinuous inner ring 64, the bottom edge of which engages areplaceable wear plate 66 positioned in an annular recess in the lowerplate member 58. The rotor assembly also includes an annular plate 68interposed between a shoulder 70 on the upper portion of the rotor shaft38 and the lower rotor plate 58 to protect the bearing assemblies 32 and34 from dust and other foreign matter, the plate 68 acting as a slingerring when the unit is in operation.

The rotor assembly 40 and the plate 68 are tightly clamped against theshoulder 70 by a nut 72 threaded into the upper end of the shaft 38, thenut having a conical surface adapted to force a split ring 74 tightlyinto a recess 76 formed in the rotor plate 58. The upper surface of thenut 72 is suitably formed to facilitate the flow of material from theinlet funnel 22 into the rotor as more fully explained below.

To maintain the upper and lower surfaces of the rotor assembly 40 andthe spaces between the rotor assembly and the adjacent stationary partsfree from particles these areas are continuously swept by a flow ofpressurized air. For this purpose air is supplied -at a pressure of from40 to 120 psi. through an inlet opening 78 in the funnel 22 and flowsthrough a passage 80 and thence through a series of small orifices 82 ina wear plate 84 carried by the top cover 18 and flows into the spacebetween the plate 84 and the adjacent surface of the upper rotor plate56.'Similarly, pressurizedair is supplied through an opening 86 in thehousing wall 28 and flows through an annular passage 88 in an annularblock 90 secured by screws 92 to the upper surface of the housing wall28.

Air passes from the annular channel 88 through a plurality of ports 93into the clearance space between the top of the block 90 and the lowersurface of the rotor assembly 40 for passage into the chamber 26.Cleanout ports 94 extend through the housing wall 28 for the removal ofdirt and dust from the rotor area. Positioned within the chamber 26 isan annular impact or target assembly 96 held against locating surfaceson a support plate 98 clamped between the target assembly 96 and thetop. cover 18 by a series of screws 100.

As shown in FIGS. 1 and 2 target assembly 96 comprises individual impacttargets or blocks 114 with target surfaces 115, the targets being brazedto upper and lower support rings 116 and 118, respectively, and spacedfrom each other to provide passages 117 in the device for escape ofmaterial radially outwardly away from the'rotor after striking thetargets 114. The provision of lower support ring 118 in addition toupper ring 116 adds stability to the target assembly and preventscracking of the targets 114.

Tangential outlet 119 is provided to exhaust the comminuted materialfrom chamber 106.

Formed within the top plate 56 of rotor assembly 40 are radiallyextending channels 120 which are open at their outer ends to communicatewith impact chamber 26 and at their inner ends to communicate with anannular inlet throat 122 at the center of the rotor immediately belowfunnel 22. The channels are formed symmetrically about a radius of therotor and progressively decrease in cross section from the center to theperiphery of the rotor to accelerate the air and particles travellingtherethrough. At least three channels 120 are provided and, in thepreferred embodiment, four such channels are utilized. The walls ofchannel 120 are formed by ribs 123 which project downwardly from therotor plate 56. The trail- I ing edges of the channels are lined withreplaceable wear plates 124 clamped in place vertically by a force fitbetween rotor plates 56 and 58 and radially by a protrusion 126 on "Asshown in FIG. 3, the wear strips 124 are U-shaped to provide aflat-bottomed wear surface 130 between flanges 132 and 134, which abutagainst rotor members 56 and 58,respectively. The flat-bottom shapeprovides for-more uniform wear and longer life of the strips, since thematerial is distributed over the full width of the strips as it passesthrough the channel 120; i

It is apparent that the machine may be readily disassembled by removingring 21 and lifting cover 18 upwardly. This results in the simultaneousremoval of funnel 22, sleeve 24, ring 84, and target assembly 96, all ofwhich are attached to cover 18. The rotor and bearing elements are thenaccessible for repair or replacement. v

Referring to FIG. 4, the angular relationship between the targets 114and rotor channels 120 has been found to be operationally significant.The trajectory angle A at which the particles leave the channels120depends upon several factors, including the distance from the center atwhich the particle acceleration begins and the friction forces betweenthe particles and strips 124. Theoretically, if the particles start atthe exact center and there areno friction forces, the trajectory anglewould be 45, since the tangential velocity component v would be equal tothe radial velocity component u. Another factor modifying the angle A isthat the channel walls 123 are not exactly radial but extend along lineswhich pass a certain distance from the center of the rotor.

The effect of these factors is to modify the trajectory angle A toproduce in practice an angle of approximately as discussed in theHoffstrom patent.

It can be established theoretically that every particle entering therotor is given the same velocity and leaves the rotor at the same angleA, thus containing the same specific energy.

each wear plate which engages a circular recess 128 in ribs 1 Thisinvention uses the kinetic energy of the particles to produce thecomminuting effect by directing the particles against stationary targets114 which are constructed of any hard material, preferably tungstencarbide. Theoretically, the greatest force of impact and most efficientconversion of the kinetic energy occurs when the particles strike targetimpact surface 115 at an angle B of It has been discovered, however,that improved performance is obtained when the targets 1 14 are arrangedto provide an angle B of approximately 1 20, preferably 1 15 or 25 awayfrom the perpendicular of the particle trajectory. The grindingefficiency of the device is not substantially reduced because thefriction angle of the material to be ground when moved over the targetsurface is larger than 25.

This arrangement of targets 114 causes the crushed fragments of materialto flow away from the rotor radially outwardly through passages 117,thus preventing wear on the rotor periphery.

In operation, the rotor 52 is rotated to create a rotor rim velocitywithin the range of 5,000-l0,000 in./sec., it being apparent that thehigher speed of rotation produces particles of smaller size. Thematerial to be ground is fed through funnel 22 to rotor annular chamber122 and outwardly through channels 120. The flat surface 130 of channelliner 124 causes the material to be spread uniformly over the entirewidth of the surface and to impinge evenly across the entire targetsurface 115 to avoid localized wear on these parts.

The rotation of the rotor also draws air along with the material through.funnel 22, which air serves as a carrying medium for the material.Additionally, air is introduced at a pressure of 40- l 20-p.s.i.into thearea below the rotor by port 86 and passageways 88 and 92 and above therotor by port 78 and passageways 82. Substantially all of thispressurized air passes radially away from the rotor axis and intochamber 26, thus preventing any ground material from collecting withinthe rotor and bearing areas.

As the material strikes target surface 115, it is reduced in size anddirected radially outwardly through passages 117 because of the angularrelationship noted above between targets -114 and the materialtrajectory angle A. The ground material and the pressurized air is thenexhausted from chamber 106 through tangential outlet 119.

The number of channels provided in the rotor is a variable dependingupon the desired capacity of the apparatus. The material enteringannular chamber 122 must immediately find an-exit channel therefrom toprevent clogging of the rotor. Also, the size of the channels must besufficient'to pass the largest particle to be ground However, asHoffstrom notes, the number of channels .should be kept to the requiredminimum to reduce the air flow through the system, since the more airthat flows, the greater will be the input energy required to move theair. Although the moving air performs a material carrying function, mostof it represents lost energy, and thus should be minimized.

It is understood then that the present invention accomplishes thedesired high efficiency and in addition provides a more stable andlonger lasting impact mill. The novel design of liner strips 124 resultsin uniform distribution of wear across surface and increases the area ofimpingement of the particles on target surface 115, thus preventing anyconcentrated gouging or wearing of these elements which would requirepremature, early discard and replacement thereof. Also, the specificstructure of the target assembly 96 maintains the high degree ofefficiency desired, while preventing wear on the periphery of the rotorby directing the comminuted particles outwardly through passages 117.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. Therefor, thepresent embodiment is to be considered illustrative and not restrictive,the scope of the invention being I claim:

1. Apparatus for reducing the size of particles comprising a housing, arotor mounted in said housing, said rotor having a plurality of channelsconnecting a center inlet section with the periphery thereof, said inletsection being open to the exterior of said housing to permit the inflowof air and particles thereto, means for rotating said rotor wherebyparticles delivered to said inlet will be moved in an airstream throughnicating with the region adjacent said target means, said airstreamdelivering broken particles to said outlet means.

2. Apparatus according to claim 1, wherein the impact surfaces of saidtargets extend at an angle of substantially more than with respect tothe path of particles issuing from said 7 channels.

3. Apparatus according to claim 1, wherein the impact surfaces of saidtargets extend at an angle of from to with respect to the path ofparticles issuing from said channels.

4. Apparatus according to claim 1 together with means for introducingpressurized air above and below said rotor and for directing said airradially outward to the region adjacent said target means, at least theflow of air below said rotor being guided along said rotor closelyadjacent the surface thereof in the region of the outer periphery ofsaid rotor, said flow of air preventing the passage of broken particlesradially inwardly towards said rotor center.

